The material properties of wide band gap (WBG) semiconductors, such as, for example, silicon carbide (SiC) or gallium nitride (GaN), permit operation at much higher voltages, frequencies, and temperatures than conventional semiconductors, including those made of silicon (Si) or gallium arsenide (GaAs). These features can lead to smaller and more energy-efficient circuits. Recently, WBG semiconductor devices are increasingly being used in high power applications, like high-speed switching for power modules and in charging modules for hybrid and all-electric vehicles.
One challenge facing most applications of WBG devices, including hard-switched power converter or inverter applications, is the occurrence of high frequency (e.g., greater than 30 megahertz (MHz)) ringing, or oscillations, during switching. This high frequency ringing induces electromagnetic interference (EMI) noises to surrounding circuitry (such as, e.g., control lines and measurement lines), as well as other sub-system components, thereby affecting overall system performance. The ringing is primarily caused by high voltage (dv/dt) and current (di/dt) transients induced by the WBG device during switching, which excites parasitic inductance (L) and capacitance (C) in the circuit, thereby causing the device to oscillate during switching.
Existing solutions for minimizing parasitic inductance in WBG devices include improving a packaging of the devices, for example, by reducing stray inductance resulting from the packaging. However, this solution can be expensive and difficult to achieve, especially in power modules rated for more than 300 amperes (A) and designed for use in hybrid and electric vehicles. Also, reducing packaging stray inductance does not eliminate the ringing that occurs during switching. Another existing solution attempts to minimize the ringing by adding external passive components, such as R/C (snubber circuits), to absorb the ringing energy. However, this solution requires the use of additional components, increases packaging cost and size, and reduces reliability during high temperature operation. In addition, the introduction of additional resistors and other external passive components reduces the device dv/dt, di/dt speeds, which in turn greatly increases the switching loss of the device. Another downside of these and other similar existing solutions is that they require external modifications to the WBG device that cannot be controlled or adjusted to manipulate the amount of ringing.
Accordingly, there is still a need in the art for techniques to minimizing ringing or oscillations in wide band gap semiconductor devices during high speed switching.